1. Field of the Invention
The present invention relates to a recording material having a layer of a photopolymerizable composition.
2. Description of the Prior Art
As photoresist materials for making printed circuits, recording materials of the solution processing type have commonly been used, such as photosensitive liquids comprising a combination of dichromate and glue, poly(vinyl alcohol), or the like; photosensitive liquids comprising, as main components, poly(vinyl cinnamate) and a sensitizer; photosensitive liquids comprising, as main components, natural or cyclized rubber and a cross linking agent; and the like.
Still other recording materials of the solution processing type are those having a structure where a photosensitive layer is sandwiched between two plastic films. Upon the use of this kind of recording material, one of the films is stripped off to expose the photosensitive layer, the photosensitive layer is laminated on a desired base for a printed circuit, e.g., copper, and the resulting laminate is image-wise exposed through the remaining plastic film. Thereafter, the plastic film is removed, and the laminate is subjected to development in an appropriate developing solution such as an organic solvent, an aqueous alkaline solution, and the like, whereby exposed or cured parts remain on the copper base and unexposed or uncured parts are washed off into the developing solution to produce a resist pattern of the desired printed circuit. The above-described recording materials of the solution processing type, however, are cumbersome due to the use of processing solutions. In addition, the use of processing solutions is apt to cause environmental hazards.
A new type of recording material has been proposed in recent years which is capable of forming images by a dry processing utilizing the difference in adhesion to a base between exposed and unexposed areas, as described in Japanese Patent Publications No. 22,901/68 and 7,728/72. In general, this type of recording material comprises a base, for example, of plastic, metal or paper; a layer of a photopolymerizable composition containing as the principal components a polymeric binder, an unsaturated monomer, and a photopolymerization inhibitor; and a thin, transparent cover film. After exposure to an original, the cover film is peeled off to give both negative and positive (or positive and negative) images on the surfaces of the base and the film, whereby either exposed or unexposed parts of the composition remain on the base. By the use of this type of recording material, a resist pattern can be produced merely by peeling off the cover film while omitting processing in liquids as required with solution processing type recording materials. From this, a substantial savings in labor can be expected in producing printed circuits. In addition, stripping and removing can also be carried out with great ease as compared with earlier recording materials. Needless to say, this is a highly advanced technique. In the production of resist patterns according to this method, the photosensitive layer must be destroyed along boundary lines between exposed and unexposed parts, so the properties of the polymeric binding agents and monomers used are of great importance. In particular, the properties of the polymeric binder such as molecular weight, softening point, crystallinity, miscibility with other components, adhesiveness to the base, and the like are of particular importance. In addition, the formed images, which are used for a variety of uses, preferably possess properties required for their end use such as wear-resistance, chemical-resistance and weather resistance.
The quality of the materials used in photosensitive materials of the type comprising a combination of a polymeric binding agent, a monomer, and a polymerization initiator are also of great importance. However, materials used in the prior art do not always possess satisfactory properties, and hence do not always give images of satisfactory quality. For example, it is described in Japanese Patent Publication No. 9,663/63 that such polymeric materials can be used as a binder and may serve to raise the tackiness of the photosensitive layer to the substrate (e.g., a copper-coated plate) or the support, e.g., polyvinyl butyral, polyvinyl acetate, polyvinyl pyrrolidone, gelatin, coumarone-indene resins, silicone resins, rubbers, etc., and it is described in Japanese Patent Publication No. 7,728/72 that polymeric materials such as vinylidene chloride copolymers, cellulose ethers, synthetic rubbers, polyvinyl acetate copolymers, polyacrylate, polyvinyl chloride, etc. can be used as a binder. However, satisfactory results were not always obtained in actual experiments conducted using these polymeric materials in combination with various kinds of monomers and polymerization initiators.